Make the node graph's "Merge Selected Nodes" target the right-clicked node, and fix it crashing

[Keavon]

Fixes #4250.

[cubic-dev-ai]

No issues found across 4 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Re-trigger cubic}

[gemini-code-assist]

Code Review

This pull request introduces several improvements and bug fixes to the node graph and document management systems. It adds a test to ensure merging un-exported nodes during inspection does not crash, updates right-click behavior to auto-select unselected nodes for context actions, and prevents dangling monitor node inputs by verifying subnetwork exports before monitoring. Additionally, it refactors the document name generation logic. Feedback is provided regarding a potential naming collision bug in the document name generation logic, where the binary search on a transformed array with duplicates can behave unpredictably; a simpler linear scan is suggested instead.

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